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Willis, Sarah J.
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Publications (10 of 36) Show all publications
Cheng, A. J., Willis, S. J., Zinner, C., Chaillou, T., Ivarsson, N., Ørtenblad, N., . . . Westerblad, H. (2017). Post-exercise recovery of contractile function and endurance in humans and mice is accelerated by heating and slowed by cooling skeletal muscle. Journal of Physiology, 595(24), 7413-7426
Open this publication in new window or tab >>Post-exercise recovery of contractile function and endurance in humans and mice is accelerated by heating and slowed by cooling skeletal muscle
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2017 (English)In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 595, no 24, p. 7413-7426Article in journal (Refereed) Published
Abstract [en]

Key points: We investigated whether intramuscular temperature affects the acute recovery of exercise performance following fatigue-induced by endurance exercise. Mean power output was better preserved during an all-out arm-cycling exercise following a 2 h recovery period in which the upper arms were warmed to an intramuscular temperature of ˜ 38°C than when they were cooled to as low as 15°C, which suggested that recovery of exercise performance in humans is dependent on muscle temperature. Mechanisms underlying the temperature-dependent effect on recovery were studied in intact single mouse muscle fibres where we found that recovery of submaximal force and restoration of fatigue resistance was worsened by cooling (16-26°C) and improved by heating (36°C). Isolated whole mouse muscle experiments confirmed that cooling impaired muscle glycogen resynthesis. We conclude that skeletal muscle recovery from fatigue-induced by endurance exercise is impaired by cooling and improved by heating, due to changes in glycogen resynthesis rate.

Manipulation of muscle temperature is believed to improve post-exercise recovery, with cooling being especially popular among athletes. However, it is unclear whether such temperature manipulations actually have positive effects. Accordingly, we studied the effect of muscle temperature on the acute recovery of force and fatigue resistance after endurance exercise. One hour of moderate-intensity arm cycling exercise in humans was followed by 2 h recovery in which the upper arms were either heated to 38°C, not treated (33°C), or cooled to ∼15°C. Fatigue resistance after the recovery period was assessed by performing 3 × 5 min sessions of all-out arm cycling at physiological temperature for all conditions (i.e. not heated or cooled). Power output during the all-out exercise was better maintained when muscles were heated during recovery, whereas cooling had the opposite effect. Mechanisms underlying the temperature-dependent effect on recovery were tested in mouse intact single muscle fibres, which were exposed to ∼12 min of glycogen-depleting fatiguing stimulation (350 ms tetani given at 10 s interval until force decreased to 30% of the starting force). Fibres were subsequently exposed to the same fatiguing stimulation protocol after 1-2 h of recovery at 16-36°C. Recovery of submaximal force (30 Hz), the tetanic myoplasmic free [Ca2+] (measured with the fluorescent indicator indo-1), and fatigue resistance were all impaired by cooling (16-26°C) and improved by heating (36°C). In addition, glycogen resynthesis was faster at 36°C than 26°C in whole flexor digitorum brevis muscles. We conclude that recovery from exhaustive endurance exercise is accelerated by raising and slowed by lowering muscle temperature.

Keywords
Cold-water immersion, Fatigue, Glycogen, Recovery, Skeletal muscle, Temperature
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-32275 (URN)10.1113/JP274870 (DOI)000418228800014 ()28980321 (PubMedID)2-s2.0-85031895429 (Scopus ID)
Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2018-02-22Bibliographically approved
Born, D.-P. -., Faiss, R., Willis, S. J., Strahler, J., Millet, G. P., Holmberg, H.-C. & Sperlich, B. (2016). Circadian variation of salivary immunoglobin A, alpha-amylase activity and mood in response to repeated double-poling sprints in hypoxia. European Journal of Applied Physiology, 116(1), 1-10
Open this publication in new window or tab >>Circadian variation of salivary immunoglobin A, alpha-amylase activity and mood in response to repeated double-poling sprints in hypoxia
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2016 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 116, no 1, p. 1-10Article in journal (Refereed) Published
Abstract [en]

Purpose: To assess the circadian variations in salivary immunoglobin A (sIgA) and alpha-amylase activity (sAA), biomarkers of mucosal immune function, together with mood during 2 weeks of repeated sprint training in hypoxia (RSH) and normoxia (RSN). Methods: Over a 2-week period, 17 competitive cross-country skiers performed six training sessions, each consisting of four sets of five 10-s bouts of all-out double-poling under either normobaric hypoxia (FiO2: 13.8 %, 3000 m) or normoxia. The levels of sIgA and sAA activity and mood were determined five times during each of the first (T1) and sixth (T6) days of training, as well as during days preceding (baseline) and after the training intervention (follow-up). Results: With RSH, sIgA was higher on T6 than T1 (P = 0.049), and sAA was increased on days T1, T6, and during the follow-up (P < 0.01). With RSN, sIgA remained unchanged and sAA was elevated on day T1 only (P = 0.04). Similarly, the RSH group demonstrated reduced mood on days T1, T6, and during the follow-up, while mood was lowered only on T1 with RSN (P < 0.01). Conclusions: The circadian variation of sIgA and sAA activity, biomarkers of mucosal immune function, as well as mood were similar on the first day of training when repeated double-poling sprints were performed with or without hypoxia. Only with RSH did the levels of sIgA and sAA activity rise with time, becoming maximal after six training sessions, when mood was still lowered. Therefore, six sessions of RSH reduced mood, but did not impair mucosal immune function. © 2015, Springer-Verlag Berlin Heidelberg.

Keywords
Circadian rhythm, Diurnal profile, Mood state, Psycho-immunological stress-response, XC skiing
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-26908 (URN)10.1007/s00421-015-3236-3 (DOI)000367610200001 ()2-s2.0-84952980085 (Scopus ID)
Note

CODEN: EJAPF

Available from: 2016-01-25 Created: 2016-01-25 Last updated: 2017-11-30Bibliographically approved
Kazior, Z., Willis, S. J., Moberg, M., Apro, W., Calbet, J. A. L., Holmberg, H.-C. & Blomstrand, E. (2016). Endurance Exercise Enhances the Effect of Strength Training on Muscle Fiber Size and Protein Expression of Akt and mTOR. PLoS ONE, 11(2), Article ID e0149082.
Open this publication in new window or tab >>Endurance Exercise Enhances the Effect of Strength Training on Muscle Fiber Size and Protein Expression of Akt and mTOR
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2016 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 2, article id e0149082Article in journal (Refereed) Published
Abstract [en]

Reports concerning the effect of endurance exercise on the anabolic response to strength training have been contradictory. This study re-investigated this issue, focusing on training effects on indicators of protein synthesis and degradation. Two groups of male subjects performed 7 weeks of resistance exercise alone (R; n = 7) or in combination with preceding endurance exercise, including both continuous and interval cycling (ER; n = 9). Muscle biopsies were taken before and after the training period. Similar increases in leg-press 1 repetition maximum (30%; P< 0.05) were observed in both groups, whereas maximal oxygen uptake was elevated (8%; P< 0.05) only in the ER group. The ER training enlarged the areas of both type I and type II fibers, whereas the R protocol increased only the type II fibers. The mean fiber area increased by 28% (P< 0.05) in the ER group, whereas no significant increase was observed in the R group. Moreover, expression of Akt and mTOR protein was enhanced in the ER group, whereas only the level of mTOR was elevated following R training. Training-induced alterations in the levels of both Akt and mTOR protein were correlated to changes in type I fiber area (r = 0.55-0.61, P< 0.05), as well as mean fiber area (r = 0.55-0.61, P< 0.05), reflecting the important role played by these proteins in connection with muscle hypertrophy. Both training regimes reduced the level of MAFbx protein (P< 0.05) and tended to elevate that of MuRF-1. The present findings indicate that the larger hypertrophy observed in the ER group is due more to pronounced stimulation of anabolic rather than inhibition of catabolic processes.

National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-27816 (URN)10.1371/journal.pone.0149082 (DOI)000371218400061 ()26885978 (PubMedID)2-s2.0-84960336508 (Scopus ID)
Available from: 2016-06-08 Created: 2016-06-07 Last updated: 2017-11-30Bibliographically approved
Larsen, F. J., Schiffer, T. A., Örtenblad, N., Zinner, C., Morales-Alamo, D., Willis, S. J., . . . Boushel, R. (2016). High-intensity sprint training inhibits mitochondrial respiration through aconitase inactivation. The FASEB Journal, 30(1), 417-427
Open this publication in new window or tab >>High-intensity sprint training inhibits mitochondrial respiration through aconitase inactivation
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2016 (English)In: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 30, no 1, p. 417-427Article in journal (Refereed) Published
Abstract [en]

Intense exercise training is a powerful stimulus that activates mitochondrial biogenesis pathways and thus increases mitochondrial density and oxidative capacity. Moderate levels of reactive oxygen species (ROS) during exercise are considered vital in the adaptive response, but high ROS production is a serious threat to cellular homeostasis. Although biochemical markers of the transition from adaptive to maladaptive ROS stress are lacking, it is likely mediated by redox sensitive enzymes involved in oxidative metabolism. One potential enzyme mediating such redox sensitivity is the citric acid cycle enzyme aconitase. In this study, we examined biopsy specimens of vastus lateralis and triceps brachii in healthy volunteers, together with primary human myotubes. An intense exercise regimen inactivated aconitase by 55-72%, resulting in inhibition of mitochondrial respiration by 50-65%. In the vastus, the mitochondrial dysfunction was compensated for by a 15-72% increase in mitochondrial proteins, whereas H2O2 emission was unchanged. In parallel with the inactivation of aconitase, the intermediary metabolite citrate accumulated and played an integral part in cellular protection against oxidative stress. In contrast, the triceps failed to increase mitochondrial density, and citrate did not accumulate. Instead, mitochondrial H2O2 emission was decreased to 40% of the pretraining levels, together with a 6-fold increase in protein abundance of catalase. In this study, a novel mitochondrial stress response was highlighted where accumulation of citrate acted to preserve the redox status of the cell during periods of intense exercise.

Keywords
exercise, mitochondrial dysfunction, reactive oxygen species, citrate
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-27824 (URN)10.1096/fj.15-276857 (DOI)000367621000039 ()26452378 (PubMedID)2-s2.0-84973472750 (Scopus ID)
Available from: 2016-06-08 Created: 2016-06-07 Last updated: 2017-08-09Bibliographically approved
Gejl, K. D., Hvid, L. G., Willis, S. J., Andersson, E., Holmberg, H.-C., Jensen, R., . . . Ortenblad, N. (2016). Repeated high-intensity exercise modulates Ca2+ sensitivity of human skeletal muscle fibers. Scandinavian Journal of Medicine and Science in Sports, 26(5), 488-497
Open this publication in new window or tab >>Repeated high-intensity exercise modulates Ca2+ sensitivity of human skeletal muscle fibers
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2016 (English)In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 26, no 5, p. 488-497Article in journal (Refereed) Published
Abstract [en]

The effects of short-term high-intensity exercise on single fiber contractile function in humans are unknown. Therefore, the purposes of this study were: (a) to access the acute effects of repeated high-intensity exercise on human single muscle fiber contractile function; and (b) to examine whether contractile function was affected by alterations in the redox balance. Eleven elite cross-country skiers performed four maximal bouts of 1300m treadmill skiing with 45min recovery. Contractile function of chemically skinned single fibers from triceps brachii was examined before the first and following the fourth sprint with respect to Ca2+ sensitivity and maximal Ca2+-activated force. To investigate the oxidative effects of exercise on single fiber contractile function, a subset of fibers was incubated with dithiothreitol (DTT) before analysis. Ca2+ sensitivity was enhanced by exercise in both MHC I (17%, P<0.05) and MHC II (15%, P<0.05) fibers. This potentiation was not present after incubation of fibers with DTT. Specific force of both MHC I and MHC II fibers was unaffected by exercise. In conclusion, repeated high-intensity exercise increased Ca2+ sensitivity in both MHC I and MHC II fibers. This effect was not observed in a reducing environment indicative of an exercise-induced oxidation of the human contractile apparatus.

Keywords
Sprint skiing, muscle fiber, specific force, fatigue
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-27809 (URN)10.1111/sms.12483 (DOI)000375077800002 ()25944268 (PubMedID)2-s2.0-84946189228 (Scopus ID)
Available from: 2016-06-08 Created: 2016-06-07 Last updated: 2017-11-30Bibliographically approved
Zinner, C., Morales-Alamo, D., Örtenblad, N., Larsen, F. J., Schiffer, T. A., Willis, S. J., . . . Holmberg, H.-C. (2016). The Physiological Mechanisms of Performance Enhancement with Sprint Interval Training Differ between the Upper and Lower Extremities in Humans. Frontiers in Physiology, 7(SEP), Article ID 426.
Open this publication in new window or tab >>The Physiological Mechanisms of Performance Enhancement with Sprint Interval Training Differ between the Upper and Lower Extremities in Humans
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2016 (English)In: Frontiers in Physiology, ISSN 1664-042X, E-ISSN 1664-042X, Vol. 7, no SEP, article id 426Article in journal (Refereed) Published
Abstract [en]

To elucidate the mechanisms underlying the differences in adaptation of arm and leg muscles to sprint training, over a period of 11 days 16 untrained men performed six sessions of 4-6 x 30-s all-out sprints (SIT) with the legs and arms, separately, with a 1-h interval of recovery. Limb-specific VO(2)peak, sprint performance (two 30-s Wingate tests with 4-min recovery), muscle efficiency and time-trial performance (TT, 5-min all-out) were assessed and biopsies from the m. vastus lateralis and m. triceps brachii taken before and after training. VO(2)peak and Wmax increased 3-11% after training, with a more pronounced change in the arms (P < 0.05). Gross efficiency improved for the arms (+8.8%, P < 0.05), but not the legs (-0.6%). Wingate peak and mean power outputs improved similarly for the arms and legs, as did TT performance. After training, VO2 during the two Wingate tests was increased by 52 and 6% for the arms and legs, respectively (P < 0.001). In the case of the arms, VO2 was higher during the first than second Wingate test (64 vs. 44%, P < 0.05). During the TT, relative exercise intensity, HR, VO2, VCO2, V-E, and V-t were all lower during arm-cranking than leg-pedaling, and oxidation of fat was minimal, remaining so after training. Despite the higher relative intensity, fat oxidation was 70% greater during leg-pedaling (P = 0.017). The aerobic energy contribution in the legs was larger than for the arms during the Wingate tests, although VO2 for the arms was enhanced more by training, reducing the O-2 deficit after SIT. The levels of muscle glycogen, as well as the myosin heavy chain composition were unchanged in both cases, while the activities of 3-hydroxyacyl-CoA-dehydrogenase and citrate synthase were elevated only in the legs and capillarization enhanced in both limbs. Multiple regression analysis demonstrated that the variables that predict TT performance differ for the arms and legs. The primary mechanism of adaptation to SIT by both the arms and legs is enhancement of aerobic energy production. However, with their higher proportion of fast muscle fibers, the arms exhibit greater plasticity.

Keywords
high-intensity training, lower body, performance, triceps brachii, upper body
National Category
Health Sciences
Identifiers
urn:nbn:se:miun:diva-29136 (URN)10.3389/fphys.2016.00426 (DOI)000384362100001 ()2-s2.0-84992110579 (Scopus ID)
Available from: 2016-10-27 Created: 2016-10-27 Last updated: 2017-11-29Bibliographically approved
Fabré, N., Mourot, L., Zoppirolli, C., Andersson, E., Willis, S. J. & Holmberg, H.-C. (2015). Alterations in aerobic energy expenditure and neuromuscular function during a simulated cross-country skiathlon with the skating technique. Human Movement Science, 40, 326-340
Open this publication in new window or tab >>Alterations in aerobic energy expenditure and neuromuscular function during a simulated cross-country skiathlon with the skating technique
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2015 (English)In: Human Movement Science, ISSN 0167-9457, E-ISSN 1872-7646, Vol. 40, p. 326-340Article in journal (Refereed) Published
Abstract [en]

Here, we tested the hypothesis that aerobic energy expenditure (AEE) is higher during a simulated 6-km (2 loops of 3-km each) "skiathlon" than during skating only on a treadmill and attempted to link any such increase to biomechanical and neuromuscular responses. Six elite male cross-country skiers performed two pretesting time-trials (TT) to determine their best performances and to choose an appropriate submaximal speed for collection of physiological, biomechanical and neuromuscular data during two experimental sessions ((exp)). Each skier used, in randomized order, either the classical (CL) or skating technique (SK) for the first 3-km loop, followed by transition to the skating technique for the second 3-km loop. Respiratory parameters were recorded continuously. The EMG activity of the triceps brachii (TBr and vastus lateralis (VLa) muscles during isometric contractions performed when the skiers were stationary (i.e., just before the first loop, during the transition, and after the second loop); their corresponding activity during dynamic contractions; and pole and plantar forces during the second loop were recorded. During the second 3-km of the 'IT, skating speed was significantly higher for the SK-SK than CL-SK. During this second loop, AEE was also higher (+1.5%) for CL-SKexp than SK-SKexp, in association with higher VLa EMG activity during both isometric and dynamic contractions, despite no differences in plantar or pole forces, poling times or cycle rates. Although the underlying mechanism remains unclear, during a skiathlon, the transition between the sections of classical skiing and skating alters skating performance (i.e., skiing speed), AEE and neuromuscular function. (C) 2015 Elsevier B.V. All rights reserved.

Keywords
Cross-country skiing, EMG, Muscle fatigue, Oxygen uptake, Techniques, Transition
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-25651 (URN)10.1016/j.humov.2015.01.014 (DOI)000351978200025 ()25681656 (PubMedID)2-s2.0-84922465769 (Scopus ID)
Available from: 2015-08-28 Created: 2015-08-18 Last updated: 2017-12-04Bibliographically approved
Mourot, L., Fabre, N., Andersson, E., Willis, S., Buchheit, M. & Holmberg, H.-C. (2015). Cross-Country Skiing and Postexercise Heart-Rate Recovery. International Journal of Sports Physiology and Performance, 10(1), 11-16
Open this publication in new window or tab >>Cross-Country Skiing and Postexercise Heart-Rate Recovery
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2015 (English)In: International Journal of Sports Physiology and Performance, ISSN 1555-0265, E-ISSN 1555-0273, Vol. 10, no 1, p. 11-16Article in journal (Refereed) Published
Abstract [en]

Postexercise heart-rate (HR) recovery (HRR) indices have been associated with running and cycling endurance-exercise performance. The current study was designed (1) to test whether such a relationship also exists in the case of cross-country skiing (XCS) and (2) to determine whether the magnitude of any such relationship is related to the intensity of exercise before obtaining HRR indices. Ten elite male cross-country skiers (mean +/- SD; 28.2 +/- 5.4 y, 181 +/- 8 cm, 77.9 +/- 9.4 kg, 69.5 +/- 4.3 mL.min(-1) . kg(-1) maximal oxygen uptake [VO2max]) performed 2 sessions of roller-skiing on a treadmill: a 2 x 3-km time trial and the same 6-km at an imposed submaximal speed followed by a final 800-m time trial. VO2 and HR were monitored continuously, while HRR and blood lactate (BLa) were assessed during 2 min immediately after each 6-km and the 800-m time trial. The 6-km time-trial time was largely negatively correlated with VO2max and BLa. On the contrary, there was no clear correlation between the 800-m time-trial time and VO2, HR, or BLa. In addition, in no case was any clear correlation between any of the HRR indices and performance time or VO2max observed. These findings confirm that XCS performance is largely correlated with VO2max and the ability to tolerate high levels of BLa; however, postexercise HRR showed no clear association with performance. The homogeneity of the group of athletes involved and the contribution of the arms and upper body to the exercise preceding determination of HRR may explain this absence of a relationship.

Keywords
postexercise reactivation, time trial, performance, maximal oxygen uptake, blood lactate
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-24401 (URN)10.1123/ijspp.2013-0445 (DOI)000348486500003 ()2-s2.0-84922356343 (Scopus ID)
Available from: 2015-03-17 Created: 2015-02-20 Last updated: 2017-12-04Bibliographically approved
Stöggl, T., Bishop, P., Höök, M., Willis, S. & Holmberg, H.-C. (2015). Effect of carrying a rifle on physiology and biomechanical responses in biathletes. Medicine & Science in Sports & Exercise, 47(3), 617-624
Open this publication in new window or tab >>Effect of carrying a rifle on physiology and biomechanical responses in biathletes
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2015 (English)In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 47, no 3, p. 617-624Article in journal (Refereed) Published
Abstract [en]

Purpose: This study aimed to assess the effect of carrying a rifle on the physiological and biomechanical responses of well-trained biathletes. Methods: Ten elite biathletes (five men and five women) performed ski skating with (R) or without a rifle (NR) on a treadmill using the V2 (5- incline) and V1 techniques (8-) at 8 and 6 kmIhj1, respectively, as well as at racing intensity (approximately 95% of peak oxygen uptake (VO2peak), 10.7 T 0.8 and 7.7 T 0.9 kmIhj1, respectively). VO2, ventilation (VE), HR, blood lactate concentration (BLa), and cycle characteristics as well as pole and leg kinetics were evaluated during these trials. Results: Metabolic data were all higher for R than for NR, as follows:VO2, +2.5%;VE, +8.1%; RER, +4.2%; all P G 0.001; HR, +1.7%; and BLa, +15.1%; both P G 0.05. Biomechanically, carrying a rifle reduced cycle time and length, poling and arm swing times, and leg ground contact time and increased cycle rate, the peak and impulse of leg force, average cycle force, and impulse of forefoot force (all P G 0.05). With the exception of elevated pole forces when V2 skating at racing velocity, there were no differences between the peak and impulse of pole force. The difference inVE between R and NR was greater for the women than that for men (P G 0.05), and the difference in BLa also tended to be larger for the women (P G 0.1). Conclusions: Carrying a rifle elevated physiological responses, accelerated cycle rate, and involved greater leg work, with no differences between the V1 and V2 techniques.

Keywords
Crosscountry skiing, economy, energy cost, rifle carriage, skating
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-24609 (URN)10.1249/MSS.0000000000000438 (DOI)000349984600020 ()2-s2.0-84923614720 (Scopus ID)
Note

CODEN: MSCSB

Available from: 2015-03-17 Created: 2015-03-17 Last updated: 2017-12-04Bibliographically approved
Faiss, R., Cheng, A., Willis, S., Zinner, C., Ivarsson, N., Chaillou, T., . . . Westerblad, H. (2015). Elevated Temperature Accelerates Recovery of Mouse and Human Skeletal Muscle Following Fatigue. In: Abstract Book for the 20th Annual ECSS Congress: . Paper presented at 20th Annual ECSS Congress.
Open this publication in new window or tab >>Elevated Temperature Accelerates Recovery of Mouse and Human Skeletal Muscle Following Fatigue
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2015 (English)In: Abstract Book for the 20th Annual ECSS Congress, 2015Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

Introduction

This study was designed to determine whether elevated muscle temperature allows muscles to recover their force or power more rapidly following fatigue

Methods

Intact single fibers from mouse flexor digitorum brevis muscle were fatigued at 31˚C (70-Hz 350-ms tetani once every 10s until initial force decreased to 30%).  During a subsequent 2-hr recovery period, the fibers were perfused in Tyrode solution at either 31°C (physiological temperature) or 36°C and isometric force and cytoplasmic free [Ca2+] ([Ca2+]i) were measured during 30-Hz tetani evoked periodically.  In addition, seven human subjects performed fatiguing arm exercise consisting of 3 x 5min maximal effort arm cycling at 100 rpm followed by 4 x 15 min at an intensity of 50% of VO2peak. Then followed 2hr of recovery during which both arms were either heated or not heated at 5˚C above physiological temperatures using arm cuffs continuously perfused with temperature-regulated water; the order of heating vs. not heating was randomized between two visits. Intramuscular temperature was recorded with probes inserted 1.5 cm into the lateral head of the triceps brachii muscle. During the recovery period, subjects consumed 1.0 g/hr/kg body weight carbohydrates to support glycogen repletion. After recovery, the subjects repeated the 3 x 5 min time trials to evaluate the effect of the recovery intervention.

Results

Recovery from fatigue in mouse single fibers was dependent on muscle glycogen restoration since fibers perfused with glucose-free Tyrode did not recover contractile force (P<0.05). After 30 min of recovery, the tetanic [Ca2+]i was 107±10% and 92 ± 8% and the corresponding forces were 69±15% vs.49±14% of the initial values for the heated and non-heated muscles, respectively.  In seven human subjects, 2h of muscle heating also appeared to improve muscle recovery, leading to higher mean power output in the post-recovery arm cycling time trial than without muscle heating.

Discussion

Elevating muscle temperature by 5°C above physiological temperature accelerates recovery in mouse muscle in-vitro and in human skeletal muscle in-vivo and this appears to depend on faster muscle glycogen resynthesis following fatigue.

National Category
Physiology
Identifiers
urn:nbn:se:miun:diva-26812 (URN)
Conference
20th Annual ECSS Congress
Available from: 2016-01-04 Created: 2016-01-04 Last updated: 2018-01-10Bibliographically approved
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